GILBERT: FISHES OF THE SUBGENUS LUXILUS


these two species in Ohio. A more complete discussion of the rela-
tionships of the two forms appears in the account of cornutus and in
the section on zoogeography and phylogeny.
 LIFE HISTORY AND ECOLOGY. N. c. chrysocephalus prefers an en-
vironment similar to that of N. cornutus. Both are ordinarily found
in small to medium-sized streams having clear, weedless water, a
moderate to swift current, and alternate pools and riffles, the latter
with a gravel and/or rubble bottom. Individuals usually are found
at the head or foot of riffles, more often the latter, but tend to avoid
the riffles themselves except at spawning time. They likewise avoid
quiet water, but individuals occasionally may be found there espe-
cially if a slight current is present.
 As a rule chrysocephalus seems somewhat more tolerant than N.
cornutus of warm, turbid conditions and has replaced it in a number
of places where the environment has been so modified. The apparent
preference of chrysocephahus for warmer waters is shown by the dis-
tribution of the two species when both occupy the same stream; the
main body of the cornutus population is more apt to occur toward the
headwaters, chrysocephalus usually is more common in the lower parts
(Trautman, 1939: 285). When an obstruction was built across one
such stream (Gilbert, 1961b: 188) N. cornutus took over completely,
apparently because that segment of the population of chrysocephalus
occurring toward the headwaters could not compete successfully un-
less continually reinforced from the main population downstream.
 N. chrysocephalus is rarely found in lakes, partly because they are
 scarce throughout most of the species' range. Only to the north
 is chrysocephalus found with any consistency in standing waters, and
 here clear, gravel or rubble-bottomed, wave-washed shores are usually
 present. As in N. cornutus, spawning probably does not occur in the
 lakes themselves, but in tributary streams.
 References to food habit studies of N. cornutus listed by Adams
 and Hankinson (1928) refer in part to N. chrysocephalus. Further ac-
 counts of the food habits of chrysocephalus are discussed by Langlois
 (1954). These studies reveal no apparent differences in food habits
 between cornutus and chrysocephalus.
 Raney (1940a) described in detail the spawning behavior of N.
 cornutus and assembled the literature on breeding both in this form
 and N. chrysocephalus. This shows no essential differences in spawn-
 ing behavior between the species, a finding supported by my own
 observations and those of others (Hankinson, 1932; Lachner, 1952).
 Whatever differences exist in spawning requirements most likely in-
 volve optimum temperatures and/or ranges of spawning temperature.


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1964